High Carbon steel knives will develop a unique patina over time. This is normal and creates a layer of protection. Never leave your knife wet, it is amazing how quickly rust can develop.
1. Rinse and wipe clean after use.
2. Dry straight away, don't leave on the drainer.
3. Store safely away with a light coat of food safe oil or beeswax over the blade (and handle if made of wood).
4. Never put in a dishwasher, it will ruin the blade and break the heart of the knifemaker.
5. Most of all...mind your fingers.